1. Field of the Invention
The present invention relates to an inkjet printing apparatus, an inkjet printing method, a data generating apparatus, and a storage medium for printing an image using a printing head, equipped with a nozzle array for each of a plurality of different inks, by a plurality of scans on the same printing area on a printing medium.
2. Description of the Related Art
There is a multipass printing method for printing an image stepwisely by a plurality of printing scans onto the same printing area on the printing medium, as a printing method in the inkjet printing apparatus. This printing mode prints an image while repeating the following two operations: performing a printing scan of ejecting an ink from a printing head while moving the printing head in a main scan direction; and a conveyance operation of conveying the printing medium in a sub-scan direction by 1/N times a printing width by a single printing scan. In such multipass printing, since the printing medium is conveyed between a preceding printing scan and a next printing scan, ink droplets are provided from the printing head on the same printing area of the printing medium at intervals of a predetermined time. Therefore, in the printing medium whose adsorption speeds of pigment inks are slow, such as plain paper, since the printing can be performed while the ink droplets given thereon is being dried, fixability of the ink can be improved.
However, when the multipass printing is performed on the printing medium on whose surface a special treatment was given, such as glossy paper, a glossiness feature in the printing portion of the image may be impaired.
Generally, in the printing medium like the glossy paper, in order to improve absorption of an ink solvent and fixation of a coloring material, fine holes are provided on its surface, and a dye colorant is absorbed thereinto together with moisture through the holes. However, in the case of the pigment ink, its pigment molecule is hard to dissolve in water and is dispersed in the moisture as particulates. Since these particulates are larger than the holes of the surface of the printing medium, it is hard for the coloring material to permeate into the interior of the printing medium. That is, since the particulates of the pigment will be fixed on the surface of the printing medium while being deposited thereon, it is considered that smoothness on the surface of the printing medium is impaired and its glossiness is lost.
Furthermore, in the multipass printing, when the pigment ink whose coloring material does not permeate easily into the interior of the printing medium is used, ink droplets applied by each printing scan dries one by one on the printing medium, and are fixed while they are piled on one another. For example, in the case of the multipass printing (4-pass printing) that scans four times the same printing area on the printing medium to complete an image, layers of ink are piled up in four steps. On the other hand, in the case of the single pass printing (1-pass printing) that completes an image by scanning once the same printing area on the printing medium, the ink layer is made in a single step. Therefore, when the multipass printing is adopted, the unevenness on the surface of the printing medium becomes intense compared with the case of the single pass printing, and the glossiness feature of the surface becomes easily lost.
In the inkjet printing method, it is known that if the ink droplets applied on the printing medium by the same scan (the same pass) contact each other before fixation completes on the printing medium surface, leveling will arise, the unevenness of the printing medium surface will decrease, and its glossiness will increase.
Japanese Patent Laid-Open 2005-297212 discloses a technology of realizing suitable glossiness by altering contact probability between the two ink droplets and thereby controlling the degree of leveling. That is, according to the technology of Japanese Patent Laid-Open 2005-297212, the number of passes is altered by selecting the number of passes or a mask pattern according to the glossiness feature of the printing medium in the inkjet printing apparatus using the pigment ink, and a printing rate per pass is raised or lowered.
On the other hand, as a technique for realizing simultaneously the degree of glossiness and granularity of a printed part of an image, there is known a technology of, after printing an image with a colored ink, applying a colorless polymer to coat the image (Japanese Patent Laid-Open No. 2001-039006). Moreover, there is also known a technology of, after printing an image with a pigment ink, performing a laminating processing on it (Japanese Patent Publication No. 4062027.)
However, with the method disclosed in Japanese Patent Laid-Open No. 2005-297212, there is a possibility that beading where the ink droplets adhere each other to effect localization occurs and the granularity of the image deteriorates. Moreover, in the case where the ink dots formed beforehand inhibits permeation of the ink droplets (subsequent ink droplets) that are applied after that, there is a possibility that the subsequent inks gather to coagulate in an uncolored area of the printing medium where the ink dots are not formed. In this case, there is a possibility that the subsequent ink whose colorant concentration is high becomes bulky at the time of coagulation, which makes unevenness of the surface of the printing medium rough, increases scattered rays, and deteriorates the degree of glossiness of the surface. Furthermore, since an ink having high colorant-concentration and low lightness is conspicuous, if it localizes and coagulates, there is a possibility that the granularity of the image may deteriorate more. As a result, there is possibility that the granularity of the image deteriorates, the unevenness of the surface of the printing medium increases, and consequently an effect of improving the glossiness may be impaired. Especially, when printing an image of high density, since an ink having high colorant-concentration will be used, the unevenness of the surface of the printing medium will increase easily and the glossiness will deteriorate easily.
Moreover, by methods disclosed by Japanese Patent Laid-Open No. 2001-039006 and Japanese Patent Publication No. 4062027, since a coating processing and a laminating processing are required, there is a possibility that they invite complication, enlargement, and higher cost of the whole of the image printing system.